Bulk acoustic resonator comprising non-piezoelectric layer

Abstract

In a representative embodiment, a bulk acoustic wave (BAW) resonator structure comprises: a first electrode disposed over a substrate; a first piezoelectric layer disposed over the first electrode; a second electrode disposed over the first piezoelectric layer, wherein c-axis orientations of crystals of the first piezoelectric layer are substantially aligned with one another; a second piezoelectric layer disposed over the second electrode; a non-piezoelectric layer; and a third electrode disposed over the second piezoelectric layer.

1. A bulk acoustic wave (BAW) resonator structure, comprising:
 a first electrode disposed over a substrate; 
 a piezoelectric layer disposed over the first electrode; 
 a second electrode disposed over the first piezoelectric layer, wherein c-axis orientations of crystals of the piezoelectric layer are substantially aligned with one another; and 
 a non-piezoelectric layer disposed over the first electrode and adjacent to the piezoelectric layer, wherein an overlap of the non-piezoelectric layer with the second electrode has a width substantially equal to an integer multiple of one-quarter wavelength of a first propagating eigenmode in the non-piezoelectric layer, or greater than or equal to an inverse of an attenuation constant (1/k) of a first evanescent eigenmode in the non-piezoelectric layer. 
 
     
     
       2. A BAW resonator structure as claimed in  claim 1 , wherein the non-piezoelectric layer is polycrystalline. 
     
     
       3. A BAW resonator structure as claimed in  claim 1 , wherein the piezoelectric layer comprises a material, and the non-piezoelectric layer is a non-crystalline form of the material. 
     
     
       4. A BAW resonator structure as claimed in  claim 3 , wherein the material is aluminum nitride. 
     
     
       5. A BAW resonator structure as claimed in  claim 1 , further comprising an acoustic reflector disposed beneath the first electrode. 
     
     
       6. A BAW resonator structure as claimed in  claim 5 , wherein the acoustic reflector comprises a cavity. 
     
     
       7. A BAW resonator structure as claimed in  claim 1 , wherein the piezoelectric layer has a piezoelectric coupling coefficient (e 33 ) and the non-piezoelectric layer has a piezoelectric coupling coefficient that is less or equal to 80% of the first piezoelectric coupling coefficient. 
     
     
       8. A bulk acoustic wave (BAW) resonator structure, comprising:
 a first electrode disposed over a substrate; 
 a first piezoelectric layer disposed over the first electrode; 
 a second electrode disposed over the first piezoelectric layer, wherein c-axis orientations of crystals of the first piezoelectric layer are substantially aligned with one another; 
 a second piezoelectric layer disposed over the second electrode; 
 a non-piezoelectric layer; and 
 a third electrode disposed over the second piezoelectric layer. 
 
     
     
       9. A BAW resonator structure as claimed in  claim 8 , wherein the non-piezoelectric layer has a width that is substantially equal to an integer multiple of one-quarter wavelength of a first propagating eigenmode in the non-piezoelectric layer, or greater than or equal to an inverse of an attenuation constant (1/k) of a first evanescent eigenmode in the non-piezoelectric layer. 
     
     
       10. A BAW resonator structure as claimed in  claim 8 , wherein the non-piezoelectric layer is disposed over the first electrode and adjacent to the first piezoelectric layer. 
     
     
       11. A BAW resonator structure as claimed in  claim 8 , wherein the non-piezoelectric layer is disposed over the second electrode and adjacent to the second piezoelectric layer. 
     
     
       12. A BAW resonator structure as claimed in  claim 10 , further comprising a second non-piezoelectric layer disposed over the second electrode and adjacent to the second piezoelectric layer. 
     
     
       13. A BAW resonator as claimed in  claim 8 , wherein the non-piezoelectric layer is polycrystalline. 
     
     
       14. A BAW resonator structure as claimed in  claim 8 , wherein the first piezoelectric layer comprises a material, and the non-piezoelectric layer is a non-crystalline form of the material. 
     
     
       15. A BAW resonator structure as claimed in  claim 14 , wherein the material is aluminum nitride. 
     
     
       16. A BAW resonator structure as claimed in  claim 8 , wherein the first piezoelectric layer has a first piezoelectric coupling coefficient (e 33 ) and the non-piezoelectric layer has a piezoelectric coupling coefficient that is less or equal to 80% the first piezoelectric coupling coefficient. 
     
     
       17. A BAW resonator structure as claimed in  claim 12 , wherein the second piezoelectric layer comprises a material, and the second non-piezoelectric layer is a non-crystalline form of the material. 
     
     
       18. A BAW resonator structure as claimed in  claim 12 , wherein the second piezoelectric layer has a second piezoelectric coupling coefficient (e 33 ) and the second non-piezoelectric layer has a piezoelectric coupling coefficient that is less or equal to 80% of the second piezoelectric coupling coefficient. 
     
     
       19. A BAW resonator structure as claimed in  claim 8 , further comprising: an acoustic coupling layer disposed between the second electrode and the second piezoelectric layer; and a fourth electrode disposed above the acoustic coupling layer and beneath the second piezoelectric layer.